FIG. 32 is a sequence diagram of an X2 message exchanged between eNBs (Evolved Node Bs, radio base station apparatuses) in establishing a logical interface (an X2 interface) defined between the eNBs in a mobile communication network, specifically, a network of LTE (Long Term Evolution). Establishment of an X2 link (X2 interface) between an eNB (#1) 201 and an eNB (#2) 202 is performed as follows: either one transmits an X2 SETUP REQUEST message (step S112) and receives an X2 SETUP RESPONSE message from the other (step S113) (refer to Non Patent Literature 1).
The X2 link is set between the eNBs 201 and 202, whereby in UE (User Equipment, a mobile terminal) performing handover between the eNBs 201 and 202, the eNBs 201 and 202 exchange information using the X2 link, and thereby the handover can be achieved. If the X2 link does not exist, information exchange via an S1 interface is needed, and a time required for handover increases. In addition, burden of a core network also increases.
The logical X2 interface of an application layer is defined on an SCTP (Stream Control Transmission Protocol) (refer to Non Patent Literature 2), which is a transport layer (Non Patent Literatures 3 and 4). One SCTP association that is established in step S111 is used for one X2 link between the eNBs 201 and 202.
As one of SON (Self Organizing Network) functions that are discussed in 3GPP (3 rd Generation Partnership Project), there exists a function of an ANR (Automatic Neighbor Relation). It is one of the ANR functions that detects an eNB existing in a neighborhood, and that sets an X2 link with the neighboring eNB (refer to Non Patent Literature 5).